This invention relates to a chain wheel assembly that permits one to pedal at different speeds or at a selected speed, and particularly to an improved chain wheel assembly made of a single plate member formed with two toothed rim portions of different diameters lying in different planes, and an outermost rim to serve as a chain guard.
Earlier constructions of the chain wheel assemblies of the type described generally include at least two separate sprockets of different diameters bolted or otherwise secured together in a side-by-side relation. The construction of such chain wheel assemblies requires costly procedure and is expensive. To alleviate the problems inherent in the above-described construction, a simplified construction was proposed in U.S. Pat. No. 4,044,621, wherein a sprocket structure is formed by stamping a single piece plate member, the central portion thereof is dished and toothed at its periphery and offset to a plane parallel to that occupied by an outer annular portion which embodies a set of sprocket teeth on its outer periphery. The offset plate portions are rigidly fixed in their respective positions by bent or stepped strip-like connectors which extend from the outer periphery of the dished portion to the inner periphery of the annular portion. French Pat. No. 2 281 869 discloses another sprocket construction which also includes a single piece plate member formed to have radially spaced annular portions with sprocket teeth at their peripheries, the annular portions lying in different parallel planes and connected by bent or stepped radial strip members. In both constructions descirbed above, since the toothed annular portions are held in their positions by stepped or bent strip members, the constructions are susceptible to deformation when subjected to force, causing misalignment of parts. In addition, the hub portion of the sprocket adapted to be mounted on the pedal crank shaft generally lies out of a plane of symmetry, i.e. in a plane at one side of the parallel planes of the toothed annular portions so that the force applied on the sprocket wheel can not be uniformly distributed, this resulting in a rapid damage of the portions at which the force is localized.